The present invention, the latest in a series of developments by the present inventor, these developments having led to U.S. Pat. Nos. 5,040,187 and 5,128,951 and related application Ser. No. 07/827,884, relates to a laser diode array in which radiation is emitted from a minor surface of the array. To provide relevant background and disclosure, the foregoing patent and copending applications are incorporated herein by reference.
The inventor's work in the field started from an investigation of possible improvements to a known "Rack & Stack" assembly process for laser diode arrays, in which the inventor was involved. This technique, which still is being used rather widely today, is far more expensive than the techniques disclosed in the above-mentioned copending applications and patent.
In the "Rack & Stack" process, individual one-dimensional (1 D) subarrays are mounted on a backplane to form a two-dimensional (2 D) array. The number of individual parts involved makes it very difficult to achieve high volume production, particularly since the number of assembly steps is large, and yield has tended to be relatively low. Many of the individual assembly steps require careful alignment of the individual subarrays, contributing to longer required assembly time and lower yield. Further, the 1 D subarrays are not reworkable; if part of a subarray is flawed, the entire assembly must be scrapped, as individual laser diodes in the subarrays cannot be replaced.
Against this backdrop, prior work by the present inventor has focused on facilitating fabrication of these laser diode arrays, comprised of a plurality of laser diode bars disposed such that the radiation emitting surface of each of the laser diode bars is parallel to the upper major surface of the array substrate so as to emit radiation in a direction perpendicular to the upper major surface of the substrate. The improvements are disclosed and claimed in the referenced copending applications and patent. In the arrays according to the invention which is the subject of this application, the bars are disposed such that the radiation emitting surface of each of the laser diode bars is parallel to the minor surface of the array substrate so as to emit radiation in a direction perpendicular to the minor surface of the substrate.
Fabrication of the diodes per se is not an aspect of any of these inventions; rather, these diodes simply are commercially available products. The present inventor's work in this area has focused on types of substrates, including various techniques for providing substrates having the necessary physical and electrical characteristics. In the above-mentioned U.S. patent, a non-conductive monolithic substrate is provided with a plurality of grooves in which a metallized layer is formed to provide both electrical conductivity and an attachment surface for the laser diodes, which are soldered into the metallized grooves.
Later developments, such as disclosed in U.S. Pat. No. 5,128,951, provide a conductive substrate (such as a highly doped semiconductor), in which the metallized layer, which may be needed for attachment purposes, no longer is necessary for electrical conductivity. Instead, the conductive substrate, which may be monolithic in nature (having a doped upper portion and an undoped lower portion in one embodiment), or which may instead be of two-piece construction (having, for example, a conductive upper portion and an insulative lower portion), provides the necessary conduit for current flow to the laser diode bars.
Future array designs will require laser light emission from the minor surface of the array. The inventor has considered the desirability of providing a laser diode assembly such that light would be emitted in a direction from a minor surface of the substrate.
In the course of developing improved laser diode assemblies, the inventor also has considered different materials for use in the substrate in which the laser diode bars would be mounted. For different types of industrial and/or military applications, he has learned that different types of materials may be preferable.